Prior lost his place in the England team to Jos Buttler last summer, and then took a break from the game to address his long-standing injury.
He underwent surgery on the tendon and remains in rehab and Sussex boss Mark Robinson admits they do not know when the wicketkeeper-batsman will be back in action.
???He???s out pretty much indefinitely at the moment.??He???s still recovering from an Achilles injury which he did playing for England,??? Robinson told Sky Sports News HQ.
???It???s a blow for him and a blow for us. He???s working hard on his rehab. He???s in most days of the week. Sometimes it???s a bit soul destroying. As everybody knows, it???s been a long injury.
???We feel for him as a cricketer ??? he???s just itching to get playing again ??? and for the club too, because to have your wicketkeeper batting in the top five would have been such a bonus for us.???